Light emitting diode with three-dimensional nano-structures

ABSTRACT

A light emitting diode including a first semiconductor layer, an active layer, and a second semiconductor layer is provided. The first semiconductor layer includes a first surface and a second surface. The active layer and the second semiconductor layer are stacked on the second surface in that order, and a surface of the second semiconductor layer away from the active layer is configured as the light emitting surface. A first electrode is electrically connected with and covers the first surface of the first semiconductor layer. A second electrode is electrically connected with the second semiconductor layer. A number of three-dimensional nano-structures are located both on the first surface and second surface, and a cross section of each of the three-dimensional nano-structure is M-shaped.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/093,692, filed on Dec. 2, 2013, entitled, “LIGHT EMITTING DIODE WITHTHREE-DIMENSIONAL NANO-STRUCTURES ON A SEMICONDUCTOR LAYER AND AN ACTIVELAYER,” which is a continuation of U.S. patent application Ser. No.13/479,225, filed on May 23, 2012, entitled, “LIGHT EMITTING DIODE WITHTHREE-DIMENSIONAL NANO-STRUCTURES,” which claims all benefits accruingunder 35 U.S.C. §119 from China Patent Application No. 201110395477.0,filed on Dec. 3, 2011 in the China Intellectual Property Office. Thedisclosures of the above-identified applications are incorporated hereinby reference.

BACKGROUND

1. Technical Field

The present disclosure relates to a light emitting diode (LED).

2. Description of the Related Art

LEDs are semiconductors that convert electrical energy into light.Compared to conventional light sources, the LEDs have higher energyconversion efficiency, higher radiance (i.e., they emit a largerquantity of light per unit area), longer lifetime, higher responsespeed, and better reliability. LEDs also generate less heat. Therefore,LED modules are widely used as light sources in optical imaging systems,such as displays, projectors, and so on.

LEDs include an N-type semiconductor layer, a P-type semiconductorlayer, an active layer, an N-type electrode, and a P-type electrode. Theactive layer is located between the N-type semiconductor layer and theP-type semiconductor layer. The P-type electrode is located on theP-type semiconductor layer. The N-type electrode is located on theN-type semiconductor layer. Typically, the P-type electrode istransparent. In operation, a positive voltage and a negative voltage areapplied respectively to the P-type semiconductor layer and the N-typesemiconductor layer. Thus, holes in the P-type semiconductor layer andphotons in the N-type semiconductor layer can enter the active layer andcombine with each other to emit visible light.

However, the extraction efficiency of LEDs is low because the contactarea between the N-type semiconductor layer and the active layer is notlarge enough. Thus the electron-hole recombination density is low, andthe photons in the LED are sparse, thereby degrading the extractionefficiency.

What is needed, therefore, is a light emitting diode which can overcomethe above-described shortcomings.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with referenceto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the embodiments. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 shows a schematic view of one embodiment of an LED.

FIG. 2 is an isometric view of one embodiment of a three-dimensionalnano-structures array in the LED of FIG. 1.

FIG. 3 shows a scanning electron microscope (SEM) image of thethree-dimensional nano-structures array of FIG. 2.

FIG. 4 shows cross-sectional view along a line IV-IV of FIG. 2.

FIG. 5 shows a schematic view of the second semiconductor layer of FIG.1.

FIG. 6 shows a schematic view of another embodiment of an LED.

FIG. 7 shows a schematic view of the active layer of FIG. 6.

FIG. 8 shows a schematic view of another embodiment of an LED.

FIG. 9 shows a schematic view of another embodiment of an LED.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

Referring to FIG. 1, one embodiment of an LED 10 includes a firstsemiconductor layer 110, an active layer 120, a second semiconductorlayer 130, a first electrode 112, and a second electrode 132. The firstsemiconductor layer 110 includes a first surface and a second surfaceopposite to the first surface. The active layer 120 and the secondsemiconductor layer 130 are stacked on the second surface of the firstsemiconductor layer 110 in that order. The surface of the secondsemiconductor layer 120 away from the active layer 120 is configured asthe light emitting surface of LED 10. The second surface of the firstsemiconductor layer 110 defines a plurality of three-dimensionalnano-structures 113. The light emitting surface of LED 10 defines aplurality of three-dimensional nano structures 133. The first electrode112 is electrically connected with and covers the first surface of thefirst semiconductor layer 110, and the second electrode 132 iselectrically connected with the second semiconductor layer 130.

The first semiconductor layer 110 is an N-type semiconductor or a P-typesemiconductor. The material of the N-type semiconductor can includeN-type gallium nitride, N-type gallium arsenide, or N-type copperphosphate. The material of the P-type semiconductor can include P-typegallium nitride, P-type gallium arsenide, or P-type copper phosphate.The N-type semiconductor is configured to provide electrons, and theP-type semiconductor is configured to provide holes. The thickness ofthe first semiconductor layer 110 ranges from about 1 μm to about 5 μm.In one embodiment, the first semiconductor layer 110 is an N-typegallium nitride doped with Si. The first semiconductor layer 110includes a first surface and a second surface opposite to the firstsurface. The first surface contacts the first electrode 112. The activelayer 120 and the second semiconductor layer 130 are stacked on thesecond surface.

In one embodiment, a buffer layer (not shown) can be sandwiched betweenthe substrate and the first semiconductor layer 110. Because the firstsemiconductor layer 110 and the substrate have different latticeconstants, the buffer layer is used to reduce the lattice mismatch, thusthe dislocation density of the first semiconductor layer 110 willdecrease. The thickness of the buffer layer ranges from about 10nanometers to about 300 nanometers, and the material of the buffer layercan be GaN or AN.

Referring to FIG. 1 and FIG. 2, the second surface of the firstsemiconductor layer 110 is a patterned surface. The first semiconductorlayer 110 can be separated into a main body 110 a and a protruding part110 b and distinguished by an “interface.” The interface can besubstantially parallel with the first surface of the first semiconductorlayer 110. The interface is defined as a surface of the main body 110 ahereafter, and the protruding part 110 b extends away from the surfaceof the main body 110 a. The protruding part 110 b defines the pluralityof three-dimensional nano-structures 113, and the plurality ofthree-dimensional nano-structures 113 form the patterned surface of thefirst semiconductor layer 110. The three-dimensional nano-structure 113can be a protruding structure. The protruding structure protrudes outfrom the interface of the main body 110 a. The plurality ofthree-dimensional nano-structures 113 is a protruding structure locatedon the surface of the main body 110 a.

The plurality of three-dimensional nano-structures 113 can be arrangedside by side. Each of the three-dimensional nano-structures 113 canextend along a straight line, a curvy line, or a polygonal line. Theextending direction is substantially parallel with the surface of thefirst semiconductor layer 110. The two adjacent three-dimensionalnano-structures are arranged a certain distance apart from each other.The distance ranges from about 0 nanometers to about 1000 nanometers,such as 10 nanometers, 30 nanometers or 200 nanometers. The extendingdirection of the three-dimensional nano-structure 113 can be fixed orvaried. While the extending direction of the three-dimensionalnano-structure 113 is fixed, the plurality of three-dimensionalnano-structures 113 extends along a straight line, otherwise thethree-dimensional nano-structures 113 extends along a polygonal line ora curvy line. The cross-section of the three-dimensional nano-structure113 along the extending direction is M-shaped. Referring to FIG. 3, thethree-dimensional nano-structures 113 are a plurality of substantiallyparallel bar-shaped protruding structures extending along a straightline. The plurality of three-dimensional nano-structures 113 aresubstantially uniformly and equidistantly distributed on the entiresurface of the main body 110 a.

Also referring to FIG. 4, the three-dimensional nano-structure 113extends from one side of the semiconductor layer 110 to the oppositeside along the X direction. The Y direction is substantiallyperpendicular to the X direction and substantially parallel with thesurface of the main body 110 a. The three-dimensional nano-structure 113is a double-peak structure including two peaks. The cross-section of thedouble-peak structure is M-shaped. The first peak 1132 and the secondpeak 1134 extend substantially along the X direction. The first peak1132 includes a first surface 1132 a and a second surface 1132 b. Thefirst surface 1132 a and the second surface 1132 b intersect to form anintersection line and an included angle θ of the first peak 1132. Theintersection line can be a straight line, a curvy line, or a polygonalline. The included angle θ is greater than 0 degree and smaller than 180degrees. In one embodiment, the included angle θ ranges from about 30degrees to about 90 degrees. The first surface 1132 a and the secondsurface 1132 b can be planar, curvy, or wrinkly. In one embodiment, thefirst surface 1132 a and the second surface 1132 b are planar. The firstsurface 1132 a is intersected with the surface of the main body 110 a atan angle α. The angle α is greater than 0 degrees and less than or equalto 90 degrees. In one embodiment, the angle α is greater than 80 degreesand less than 90 degrees. The first surface 1132 a includes a sideconnected to the surface of the substrate, and extends away from themain body 110 a to intersect with the second surface 1132 b. The secondsurface 1132 b includes a side connected with the second peak 1134 andextends away from the main body 110 a at an angle β. The angle β isgreater than 0 degrees and smaller than 90 degrees.

The second peak 1134 includes a third surface 1134 a and a fourthsurface 1134 b. The structure of the second peak 1134 is substantiallythe same as that of the first peak 1132. The third surface 1134 a andthe fourth surface 1134 b intersect each other to form the includedangle of the second peak 1134. The third surface 1134 a includes a sideintersecting the surface of the main body 110 a and extends away fromthe main body 110 a to intersect the fourth surface 1134 b. The fourthsurface 1134 b includes a side intersecting the third surface 1134 a toform the included angle of the second peak 1134, and extends tointersect the second surface 1132 b of the first peak 1132 to define afirst groove 1136. A second groove 1138 is defined between two adjacentthree-dimensional nano-structures 113. The second groove 1138 is definedby the third surface 1134 a of the second peak 1134 and the firstsurface 1132 a of the first peak 1132 of the adjacent three-dimensionalnano-structure 113.

The first peak 1132 and the second peak 1134 protrude out of the mainbody 110 a. The height of the first peak 1132 and the second peak 1134is arbitrary and can be selected according to need. In one embodiment,both the height of the first peak 1132 and that of the second peak 1134range from about 150 nanometers to about 200 nanometers. The height ofthe first peak 1132 can be substantially equal to that of the secondpeak 1134. The highest points of the first peak 1132 and the second peak1134 are defined as the farthest point away from the surface of the mainbody 110 a. In one three-dimensional nano-structure 113, the highestpoint of the first peak 1132 is spaced from that of the second peak 1134a certain distance ranging from about 20 nanometers to about 100nanometers. The first peak 1132 and the second peak 1134 extendsubstantially along the X direction. The cross-section of the first peak1132 and the second peak 1134 can be trapezoidal or triangular, and theshape of the first peak 1132 and the second peak 1134 can besubstantially the same. In one embodiment, the cross-sections of thefirst peak 1132 and the second peak 1134 are triangular. In oneembodiment, the first peak 1132, the second peak 1134, and the main body110 a form an integrated structure. Because of the limitation of thetechnology, the first surface 1132 a and the second surface 1132 bcannot be absolutely planar.

In each M-shaped three-dimensional nano-structure 113, the first peak1132 and the second peak 1134 define the first groove 1136. Theextending direction of the first groove 1136 is substantially the sameas the extending direction of the first peak 1132 and the second peak1134. The cross-section of the first groove 1136 is V-shaped. The depthh₁ of the first groove 1136 in different three-dimensionalnano-structures 113 is substantially the same. The depth h₁ is definedas the distance between the highest point of the first peak 1132 and thelowest point of the first groove 1136. The depth h₁ of the first groove1136 is less than the height of the first peak 1132 and the second peak1134.

The second groove 1138 extends substantially along the extendingdirection of the three-dimensional nano-structures 113. Thecross-section of the second groove 1138 is V-shaped or an inversetrapezium. Along the extending direction, the cross-section of thesecond groove 1138 is substantially the same. The depth h₂ of the secondgrooves 1138 between each two adjacent three-dimensional nano-structures113 is substantially the same. The depth h₂ is defined as the distancebetween the highest point and the lowest point of the groove of thesecond groove 1138. The depth h₂ of the second groove 1138 is greaterthan the depth h₁ of the first groove 1136, and the ratio between h₁ andh₂ ranges from about 1:1.2 to about 1:3 (1:1.2≦h₁:h₂≦1:3). The depth ofthe first groove 1136 ranges from about 30 nanometers to about 120nanometers, and the depth of the second groove 1138 ranges from about 90nanometers to about 200 nanometers. In one embodiment, the depth of thefirst groove 1136 is about 80 nanometers, and the depth of the secondgroove 1138 is about 180 nanometers. The depth of the first groove 1136and the second groove 1138 can be selected according to need.

The width of the three-dimensional nano-structure 113 ranges from about100 nanometers to about 200 nanometers. The width of thethree-dimensional nano-structure 113 is defined as the maximum span ofthe three-dimensional nano-structure 113 along the Y direction. The spanof the three-dimensional nano-structure 113 is gradually decreased alongthe direction away from the main body 110 a. Thus in eachthree-dimensional nano-structure 113, the distance between the highestpoint of the first peak 1132 and the highest point of the second peak1134 is less than the width of the three-dimensional nano-structure 113.The plurality of three-dimensional nano-structures 113 can bedistributed in a certain interval from each other, and the intervals canbe substantially the same. The interval forms the second groove 1138.The distance λ₀ between the two adjacent three-dimensionalnano-structures 113 ranges from about 0 nanometers to about 200nanometers. The distance between each two adjacent three-dimensionalnano-structures 113 can be substantially the same. The distance λ₀ canbe increased with the increase of the height of both the first peak 1132and second peak 1134, and decreased with the decrease of the height ofboth the first 1132 and second peaks 1134. In the Y direction, thedistance λ₀ can be increased, decreased, or periodically varied. If thedistance λ₀=0, the cross-section of the second groove 1138 is V-shaped.If the distance λ₀>0, the cross-section of the second groove 1138 is inthe shape of an inverse trapezium.

Along the Y direction, the plurality of three-dimensionalnano-structures 113 is distributed in a certain period P. One period Pis defined as the width λ of the three-dimensional nano-structures 113added with the distance λ₀. The period P of the plurality ofthree-dimensional nano-structures 113 can range from about 100nanometers to about 500 nanometers. The period P, the width λ, and thedistance λ₀ satisfy the following formula: P=λ+λ₀. The period P, thewidth λ, and the distance λ₀ is measured in nanometers. The period P canbe a constant, and λ₀ or λ can be a dependent variable. Furthermore, onepart of the three-dimensional nano-structures 113 can be aligned in afirst period, and another part of the three-dimensional nano-structures113 can be aligned in a second period. In one embodiment, the period Pis about 200 nanometers, the width λ is about 190 nanometers, and thedistance λ₀ is about 10 nanometers.

The active layer 120 is located on the second surface of the firstsemiconductor layer 110. In one embodiment, the active layer 120 coversthe entire surface of the first region. The active layer 120 is engagedwith the first semiconductor layer 110. In detail, the active layer 120covers the plurality of three-dimensional nano-structures 113, and thesurface of the active layer 120 connected with the first semiconductorlayer 110 forms a patterned surface. The active layer 120 also includesa plurality of grooves and peaks, the grooves being engaged with thefirst peaks 1132 and second peaks 1134, the peaks being engaged with thefirst grooves 1136 and second grooves 1138. The active layer 120 is aphoton excitation layer and can be one of a single layer quantum wellfilm or multilayer quantum well films. The active layer 120 is made ofGaInN, AlGaInN, GaSn, AlGaSn, GaInP, or GaInSn. In one embodiment, theactive layer 120 has a thickness of about 0.3 μm and includes one layerof GaInN and another layer of GaN. The GaInN layer is stacked with theGaN layer.

Referring to FIG. 5, the second semiconductor layer 130 is located onthe active layer 120. The surface of the second semiconductor layer 130away from the active layer 120 is configured as the light emittingsurface of the LED 10. In one embodiment, the second semiconductor layer130 covers the entire surface of the active layer 120 away from thesubstrate. The thickness of the second semiconductor layer 130 rangesfrom about 0.1 μm to about 3 μm. The second semiconductor layer 130 canbe an N-type semiconductor layer or a P-type semiconductor layer.Furthermore, the type of the second semiconductor layer 130 is differentfrom the type of the first semiconductor layer 110. In one embodimentthe second semiconductor layer 130 is a P-type gallium nitride dopedwith Mg. Furthermore, the light emitting surface of the LED 10 definesthe plurality of three-dimensional nano-structures 133 to form apatterned surface. The structure of the three-dimensionalnano-structures 133 is same as the structure of the three-dimensionalnano-structures 113. The three-dimensional nano-structure 133 is aprotruding structure extending away from the second semiconductor layer130. The plurality of three-dimensional nano-structures 133 can bearranged side by side. The extending direction of the three-dimensionalnanostructures 133 can be fixed or varied. The cross-section of thethree-dimensional nanostructure 133 along the extending direction isM-shaped. Each M-shaped three-dimensional nano-structure 133 includes afirst peak 1332 and a second peak 1334 extending along the samedirection. A first groove 1336 is defined between the first peak 1332and the second peak 1334. A second groove 1338 is defined between thetwo adjacent three-dimensional nano-structures 133. The depth of thefirst groove 1336 is smaller than the depth of the second groove 1338.

The first electrode 112 is electrically connected with and covers thefirst surface of the first semiconductor layer 110. The first electrode112 is a single layer structure or a multi-layer structure. The firstelectrode 112 can also be used as the reflector of the LEDs to reflectthe photons. The first electrode 112 can be an N-type electrode or aP-type electrode according to the first semiconductor layer 110. Thematerial of the first electrode 112 can be Ti, Ag, Al, Ni, Au, or anycombination of them. The material of the first electrode 112 can also beindium-tin oxide (ITO) or carbon nanotube film. In one embodiment, thefirst electrode 112 is a two-layer structure consisted of a Ti layerwith about 15 nm in thickness and an Au layer with about 100 nm inthickness.

The second electrode 132 can be an N-type electrode or P-type electrode.In one embodiment, the second electrode 132 is located on the lightemitting surface of LED 10. In detail, the second electrode 132 coversat least part of the three-dimensional nano-structures 133. The type ofthe second electrode 132 is the same as the second semiconductor layer130. The shape of the second electrode 132 is arbitrary and can beselected according to need. The second electrode 132 covers a part ofthe surface or the entire surface of the second semiconductor layer 130.The material of the second electrode 132 can be Ti, Ag, Al, Ni, Au, orany combination of them.

Furthermore, a reflector layer (not shown) can be sandwiched between thefirst semiconductor layer 110 and the first electrode 112. The materialof the reflector can be Ti, Ag, Al, Ni, Au, or any combination thereof.The reflector includes a smooth surface having a high reflectivity. Thephotons reach the reflector and will be reflected by the reflector, thusthese photons can be extracted out of the LED 10 to improve the lightextraction efficiency of the LED 10.

The first semiconductor layer 110 includes a plurality ofthree-dimensional nano-structures to form a patterned surface, and theactive layer 120 is located on the patterned surface, thus the contactarea between the first semiconductor layer 110 and the active layer 120is enlarged. The electron-hole recombination density is improved, andthe quantity of photons is increased. The light extraction efficiency ofthe LED 10 can be improved.

One embodiment of a method for making the LED 10 includes the followingsteps:

S11, providing a substrate (not shown) with an epitaxial growth surface;

S12, growing a first semiconductor layer 110 on the epitaxial growthsurface;

S13, forming a plurality of three-dimensional nano-structures 113 on thefirst semiconductor layer 110;

S14, growing an active layer 120 and a second semiconductor layer 130 onthe surface of the plurality of three-dimensional nano-structures 113 inthat order;

S15, forming a plurality of three-dimensional nano-structures 133 byetching the surface of the second semiconductor layer 130 away from theactive layer 120;

S16, removing the substrate to expose a surface of the firstsemiconductor layer 110;

S17, applying a first electrode 112 electrically connected to andcovering the exposed surface of the first semiconductor layer 110; and

S18, locating a second electrode 132 electrically connected to thesecond semiconductor layer 130.

Referring to FIG. 6, another embodiment of an LED 20 includes a firstsemiconductor layer 110, an active layer 120, a second semiconductorlayer 130, a first electrode 112, and a second electrode 132. The firstsemiconductor layer 110 includes a first surface and an opposite secondsurface. The first surface is in contact with the first electrode 112.The active layer 120 and the second semiconductor layer 130 are stackedon the second surface, and in that order. The surface of the secondsemiconductor layer 130 away from the active layer 120 is configured asthe light emitting surface of the LED 10. The second surface of thefirst semiconductor layer defines a plurality of three-dimensionalnano-structures 113. The surface of the active layer 120 away from thefirst semiconductor layer 110 defines a plurality of three-dimensionalnano-structures 123. The light emitting surface of the LED 10 defines aplurality of three-dimensional nano-structures 133. The first electrode112 is electrically connected with the first semiconductor layer 110,and the second electrode 132 is electrically connected with the secondsemiconductor layer 130. The plurality of three-dimensionalnano-structures 123 is located on the surface of the active layer 120away from the first semiconductor layer 110. The structure of the LED 20is similar to that of the LED 10, but further includes the plurality ofthree-dimensional nano-structures 123 located on the active layer 120away form the first semiconductor layer 110.

Referring to FIG. 7, the plurality of three-dimensional nano-structures123 forms a patterned surface on the active layer 120. Thethree-dimensional nano-structure 123 is similar to the three-dimensionalnano-structures 113. Each three-dimensional nano-structure 123 includesa first peak 1232 and a second peak 1234, a first groove 1236 definedbetween the first peak 1232 and the second peak 1234, and a secondgroove 1238 defined between two adjacent three-dimensionalnano-structures 123. The distribution and alignment of thethree-dimensional nano-structures 123 is the same as the distributionand alignment of the three-dimensional nano-structures 113. The secondsemiconductor layer 130 is located on the surface of thethree-dimensional nano-structures 113, thus the surface of the secondsemiconductor layer 130 near the active layer 120 forms a patternedsurface.

In the LED 20, the surface of the active layer in contact with thesecond semiconductor layer also includes a plurality ofthree-dimensional nano-structures, thus the contact area between thesecond semiconductor layer and the active layer is also enlarged. Theelectron-hole recombination density is further increased, and the lightextraction efficiency of the LED 20 can be improved.

One embodiment of a method for making the LED 20 includes the followingsteps:

S21, providing a substrate (now shown) having an epitaxial growthsurface;

S22, growing a first semiconductor layer 110;

S23, forming a plurality of three-dimensional nano-structures 113 on asurface of the semiconductor layer 110;

S24, growing an active layer 120 on the surface of the three-dimensionalnano-structures 113, and forming a plurality of three-dimensionalnano-structures 123 on the surface away from the first semiconductorlayer 110;

S25, growing a second semiconductor layer 130 on the surface of thethree-dimensional nano-structures 123;

S26, forming a plurality of three-dimensional nano-structures 133 on thesurface of the semiconductor layer 130;

S28, removing the substrate to exposed a surface of the firstsemiconductor layer 110; and

S29, applying a first electrode 112 on the exposed surface of the firstsemiconductor layer 110, and applying a second electrode 132electrically connected to the second semiconductor layer 130.

The method of making the LED 20 is similar to the method for making theLED 10, except that the LED 20 further forms the plurality ofthree-dimensional nano-structures 123 on the surface of the active layer120 away from the first semiconductor layer 110. The substrate with thefirst semiconductor layer 110 is located in a vertical epitaxial growthreactor, and the active layer 120 grows by a vertical epitaxial growthmethod. Thus the distribution and alignment of the three-dimensionalnano-structure 123 is the same as the distribution and alignment of thethree-dimensional nano-structure 113.

Referring to FIG. 8, another embodiment of an LED 30 includes a firstsemiconductor layer 110, an active layer 120, a second semiconductorlayer 130, a first electrode 112, and a second electrode 132. The firstsemiconductor layer 110 includes a first surface and a second surfaceopposite to the first surface. The active layer 120 and the secondsemiconductor layer 130 are stacked on the second surface of the firstsemiconductor layer 110 in that order. The surface of the secondsemiconductor layer 120 away from the active layer 120 is configured asthe light emitting surface of LED 30. The second surface of the firstsemiconductor layer 110 defines a plurality of three-dimensionalnano-structures 113. The first surface of the first semiconductor layer110 defines a plurality of three-dimensional nano-structures 115. Thefirst electrode 112 is electrically connected with and covers theplurality of the three-dimensional nano-structures 115. The secondelectrode 132 is electrically connected with the second semiconductorlayer 130. The structure of the LED 30 is similar to that of the LED 10,but further includes the plurality of three-dimensional nano-structures115 located on the first surface of the first semiconductor layer 110.

The plurality of three-dimensional nano-structures 115 forms a patternedsurface. The three-dimensional nano-structure 115 is similar to thethree-dimensional nano-structures 113. The distribution and alignment ofthe three-dimensional nano-structures 115 is the same as that of thethree-dimensional nano-structures 113.

One embodiment of a method for making the LED 30 includes the followingsteps:

S31, providing a substrate;

S32, growing a first semiconductor layer 110 on the substrate;

S33, forming a plurality of three-dimensional nano-structures 113 on asurface of the semiconductor layer 110;

S34, growing an active layer 120 and a second semiconductor layer 130 onthe surface of three-dimensional nano-structures 113;

S35, removing the substrate to expose a surface of the firstsemiconductor layer 110;

S36, forming a plurality of three-dimensional nanostructures 115 on theexposed surface of the first semiconductor layer 110;

S37, applying a first electrode 112 electrically connected to and coversthe exposed surface of the first semiconductor layer 110; and

S38, applying a second electrode 132 electrically connected to thesecond semiconductor layer 130.

Photons reaching the plurality of three-dimensional nano-structures 115with a large incident angle can be reflected, changing the motiondirection of the photons so that these photons can be extracted from thelight emitting surface. Furthermore, because the three-dimensionalnano-structure 115 is M-shaped, the three-dimensional nano-structures115 can function as two layer of three-dimensional nano-structureassembled together, and the light extraction efficiency of the LED 30will be improved.

Referring to FIG. 9, another embodiment of an LED 40 includes a firstsemiconductor layer 110, an active layer 120, a second semiconductorlayer 130, a first electrode 112, and a second electrode 132. The firstsemiconductor layer 110 includes a first surface and the second surfaceopposite to the first surface. The active layer 120 and the secondsemiconductor layer 130 are stacked on the second surface of the firstsemiconductor layer 110 in that order. A surface of the secondsemiconductor layer 120 away from the active layer 120 is configured asthe light emitting surface of LED 40. The first surface of the firstsemiconductor layer 110 defines a plurality of three-dimensionalnano-structures 115. The second surface of the first semiconductor layer110 defines a plurality of three-dimensional nano-structures 113. Thesurface of the active layer 120 away from the first semiconductor layer110 defines a plurality of three-dimensional nano-structures 123. Thefirst electrode 112 is electrically connected with and covers the firstsurface of the first semiconductor layer 110, and the second electrode132 is electrically connected with the second semiconductor layer 130.The structure of the LED 40 is similar to that of the LED 30, butfurther includes the plurality of three-dimensional nano-structures 123located on the surface of the active layer 120 away from the firstsemiconductor 110.

The three-dimensional nano-structure 123 is similar to thethree-dimensional nano-structures 113. The distribution and alignment ofthe three-dimensional nano-structures 123 is the same as that of thethree-dimensional nano-structures 113

Depending on the embodiment, certain of the steps of methods describedmay be removed, others may be added, and the sequence of steps may bealtered. It is also to be understood that the description and the claimsdrawn to a method may include some indication in reference to certainsteps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

It is to be understood that the above-described embodiments are intendedto illustrate rather than limit the disclosure. Variations may be madeto the embodiments without departing from the spirit of the disclosureas claimed. It is understood that any element of any one embodiment isconsidered to be disclosed to be incorporated with any other embodiment.The above-described embodiments illustrate the scope of the disclosurebut do not restrict the scope of the disclosure.

What is claimed is:
 1. A light emitting diode, comprising: a firstsemiconductor layer having a first surface and a second surface oppositeto the first surface; an active layer stacked on the second surface; asecond semiconductor layer located on the active layer and having alight emitting surface away from the active layer; a first electrodeelectrically connected with and covering the first surface; a secondelectrode electrically connected with the second semiconductor layer;and a plurality of first three-dimensional nano-structures located onboth the first surface and the second surface, wherein each of theplurality of first three-dimensional nano-structures has a first peakand a second peak aligned side by side, a first groove is definedbetween the first peak and the second peak, a second groove is definedbetween each two adjacent first three-dimensional nano-structures of theplurality of first three-dimensional nano-structures, and a depth of thefirst groove is less than a depth of the second groove.
 2. The lightemitting diode of claim 1, wherein each of the plurality of firstthree-dimensional nano-structures is a bar-shaped protruding structureextending along a straight line, a curve line, or a polygonal line. 3.The light emitting diode of claim 1, wherein a cross-section of each ofthe plurality of first three-dimensional nano-structures has across-section of M-shaped.
 4. The light emitting diode of claim 1,wherein the first peak comprises a third surface and a fourth surfaceintersecting each other to form a first included angle, the second peakcomprises a fifth surface and a sixth surface intersecting each other toform a second included angle, and both the first included angle and thesecond included angle range from about 30 degrees to about 90 degrees.5. The light emitting diode of claim 4, wherein the first peak has afirst cross-section in a shape of a trapezoid or a triangle, and thesecond peak has a second cross-section in a shape of a trapezoid or atriangle.
 6. The light emitting diode of claim 1, wherein the activelayer is engaged with some of the plurality of first three-dimensionalnano-structures that are located on the first surface.
 7. The lightemitting diode of claim 1, wherein the plurality of firstthree-dimensional nano-structures is aligned side by side and extends toform a plurality of concentric circles or concentric rectangles.
 8. Thelight emitting diode of claim 1, wherein the plurality of firstthree-dimensional nano-structures is periodically aligned, and a periodof the plurality of first three-dimensional nano-structures ranges fromabout 100 nanometers to about 500 nanometers, the period is defined as awidth of each of the plurality of three-dimensional nano-structuresadded with a distance between adjacent two of the plurality ofthree-dimensional nanostructures.
 9. The light emitting diode of claim1, wherein a distance between the each two adjacent firstthree-dimensional nano-structures ranges from about 0 nanometers toabout 200 nanometers.
 10. The light emitting diode of claim 1, wherein awidth of each of the plurality of first three-dimensionalnano-structures ranges from about 100 nanometers to about 300nanometers.
 11. The light emitting diode of claim 1, wherein a pluralityof second three-dimensional nano-structures is further located on asurface of the active layer away from the first semiconductor layer. 12.The light emitting diode of claim 11, wherein the second semiconductorlayer is engaged with the plurality of second three-dimensionalnano-structures located on the active layer.
 13. The light emittingdiode of claim 1, further comprising a reflector located on a surface offirst semiconductor layer away from the active layer.
 14. A lightemitting diode, comprising: a first semiconductor having a first surfaceand a second surface; an active layer stacked on the second surface; asecond semiconductor layer stacked on the active layer and having alight emitting surface away from the active layer; a first electrodeelectrically connected with and covering the first surface; a secondelectrode electrically connected with the second semiconductor layer;and a plurality of first three-dimensional nano-structures located onboth the first surface and the second surface, and a plurality of secondthree-dimensional nano-structures located on at least one surface of theactive layer, wherein a cross section of each of the plurality of firstand second three-dimensional nano-structures is M-shaped.
 15. The lightemitting diode of claim 14, wherein the plurality of firstthree-dimensional nano-structures extend substantially along a firstdirection, and the plurality of second three-dimensional nano-structuresextend substantially along a second direction, and the first directionis substantially parallel with the second direction.
 16. The lightemitting diode of claim 15, wherein the first electrode covers some ofthe plurality of first three-dimensional nano-structures that arelocated on the first surface.